In the World Reference Base for Soil Resources classification scheme, a soil horizon that is thick, dark-coloured, with a base saturation of less than 50% averaged throughout the horizon, and rich in organic matter.
科学参考收录了60776条科技类词条，基本涵盖了常见科技类参考文献及英语词汇的翻译，是科学学习和研究的有利工具。